In ERPNExt fetch table field from master

In ERPNext:
fetch table field from master using following code.
But, I need this with custom script.
My code is.

  python code:

    def apply_documents_required(self):
            if self.documents_required_master:
                shipping_rule = frappe.get_doc("Documents Required Master", self.documents_required_master)
                frappe.msgprint("from python function")
                for condition in shipping_rule.get("documents_required_master"):
                    doc_req = {
                        "doctype": "Documents Required",
                        "name_of_document": condition.name_of_document,
                        "dispatch_address": condition.dispatch_address
                    }
                    if (5==5):
                        self.append("documents_required", doc_req)

js code:

    documents_required_master: function() {
            var me = this;
            msgprint("from js function")
            if(5==5) {
                return this.frm.call({
                    doc: this.frm.doc,
                    method: "apply_documents_required",
                    callback: function(r) {
                        if(!r.exc) {
                        }
                    }
                })
            }
        }